Zurich is Switzerland’s largest city, and also has one of Europe’s greatest concentration of rail infrastructure. As well as a comprehensive tramway system, it is the focal point for local, national and international railway traffic.

Current projects such as the Glattalbahn (VBG) and Tram Zurich West light rail schemes were partly aimed at dispersing demand by creating more interchanges around the metropolitan area. Handling growing demand at the main station, Zurich Hauptbahnhof (HB) remains a great challenge. Switzerland’s largest and busiest station with nearly 3,000 trains travelling daily, HB is mainly a surface terminus in the city centre.

Situated lengthways between the rivers Sihl and Limmat, it is fronted by busy tram stop, and its four-platform sub-surface station for S-Bahn trains (regional trains primarily for the Zurich region) was turned into a through route in 1991.

However, even with the adoption of multiple units and push-pull formations which save the need for locomotive changes at surface-level platforms, reversal is still a time waster and is inefficient use of platform and track space.

The project

Durchmesserlinie (the Diameter Line) Altstetten-Zurich HB-Oerlikon is the latest project to address the capacity issue. Bahnhof Oerlikon already handles traffic for the north and north-east, each main rail arteries and including services routed via Zurich Airport. Many reverse at Zurich HB for destinations in a wide arc from Basel around to the Gotthard line and Chur, with other passengers needing to change trains for onward travel.

By allowing such services to pass through the HB hub, the Durchmesserlinie project represents a large-scale reshaping of Swiss train services with implications far beyond the confines of Zurich. Moreso than the 1991 tunnel opening, this will however allow for alterations and expansion of the S-Bahn services that account for a large proportion of train movements in the area, eventually adding long-distance trains. The symbolic groundbreaking for the project was in September 2007.

The Durchmesserlinie (DML) cross-city line from Wiedikon via the Löwenstrasse station to Oerlikon was opened for passenger services in June 2014. Construction of this section took seven years to complete. The section between Löwenstrasse station and Altstetten is expected to open in December 2015.

Infrastructure

Broadly describing an ‘S’ shape to link the end points yet incorporating Zurich HB, the Durchmesserlinie is 9.6km (six miles) long. The 4.8km (three miles) long Weinberg tunnel built for the cross-city link is the core of the project. Construction of a new viaduct linking the tunnel to the main line running westwards to Altstetten is expected to be completed by 2015. It will allow the Löwenstrasse platforms to be served by 40 long-distance and 320 commuter trains a day.

“Zurich uses a mix of rolling stock for S-Bahn services, including rebuilt RBe 540 EMUs mainly dating from the 1960s.”

Leaving the existing intensively used mainline via a reconfigured portal south of Oerlikon station, the twin-track tunnel passes beneath the Limmat before broadening to a four-platform layout at a new Zurich HB Löwenstrasse station 16m beneath the main platforms, regaining the surface west of HB.

Bahnhof Alstetten marks the western limit of the project, a busy suburban interchange that will also be the western terminus of the new Tram Zurich West development.

As part of the national rail infrastructure, the line is fitted with 15kV AC electrification. Met from national and regional public funds, the project cost estimate was CHF2.03bn ($2.01bn) according to 2005 prices.

Rolling stock

Zurich uses a mix of rolling stock for S-Bahn services, including rebuilt RBe 540 EMUs mainly dating from the 1960s. Responding to growing traffic and service expansion, double-deck DPZ stock operated in push-pull mode with Re 450 single-ended locomotives was introduced from 1989.

In parallel with the Durchmesserlinie, the S-Bahn was re-equipped, the earlier high-capacity stock being due for upgrading. Entering public service in 2006, 60 Siemens RABe 514 140km/h (88mph) double-deck multiple units were ordered. A Siemens/Bombardier consortium announced an order in September 2008 to supply 113 low-floor intermediate double-deck coaches to strengthen existing S-Bahn formations.

In June 2008, an order was placed with Swiss company Stadler to supply 50 six-car double-deck electric multiple units of a new design, with options for more under the contract. Compatible for operation with existing S-Bahn stock, they will have a capacity for 1,694 passengers (526 seated) and have a top speed of 160km/h (100mph).

Signalling and communications

Switzerland is a European leader for implementing the European Rail Traffic Management System (ERTMS) project and the new line is equipped as an integral part of the principal route network. Nine emergency escape and access points are built on the tunnel section. SBB operated an information centre and held site visits to explain the works and acted as public relations for the project.

The future

For long-distance internal services such as St Gallen-Geneva, the project should save up to 30min from present schedules. Upon project completion, the temporary ‘Sihlpost’ surface platforms 51-54 added for S-Bahn use at the south side of Zurich HB should be abandoned.